Splitting / matching faces on cone to get the faces to match when wrapped around
The 2 vertical edges are ripped:

If I select a vertex, here is what it gives (so you can't join the 2 opposite vertices):

So you need to delete these 4 faces + one horizontal edge that is under the faces (as pointed out by Batfinger, probably the result of a fill (F):

Then select the top and bottom row of vertices and press CtrlF &gt; Grid Fill: